Coumadin is considered a high risk drug. Any misuse or overdose of this drug may lead to harm or injury. Coumadin use is also monitored by certain blood test. It is required that PT(prothrombin time)/INR(international ratio) be checked periodically to insure the drugs therapeutic blood level. Coumadin may be taken any time of the day but because it is highly dose dependent towards the result of PT/INR, clinicians recommend that Coumadin be taken on the same day each day specifically in the evening or night for SAFETY reason. Blood works are usually drawn in the morning including PT/INR, physicians make sure results are in before taking any dose that day. Whether results are subtherapeutic, therapeutic or supratherapeutic, dosages are adjusted or held accordingly. An INR of 2-3 is considered therapeutic for afib, PE and DVT but usually higher for artificial valve.